Interpreting Carnivore Scent-station Surveys

Glen A. Sargeant¹, Douglas H. Johnson¹, and William E. Berg²

Abstract: The scent-station survey method has been widely used to estimate trends in carnivore abundance. However, statistical properties of scent-station data are poorly understood, and the relation between scent-station indices and carnivore abundance has not been adequately evaluated. We assessed properties of scent-station indices by analyzing data collected in Minnesota during 1986-93. Visits to stations separated by <2 km were correlated for all species because individual carnivores sometimes visited several stations in succession. Thus, visits to stations had an intractable statistical distribution. Dichotomizing results for lines of 10 stations (0 or ≥1 visits) produced binomially distributed data that were robust to multiple visits by individuals. We abandoned 2-way comparisons among years in favor of tests for population trend, which are less susceptible to bias, and analyzed results separately for biogeographic sections of Minnesota because trends differed among sections. Before drawing inferences about carnivore population trends, we reevaluated published validation experiments. Results implicated low statistical power and confounding as possible explanations for equivocal or conflicting results of validation efforts. Long-term trends in visitation rates probably reflect real changes in populations, but poor spatial and temporal resolution, susceptibility to confounding, and low statistical power limit the usefulness of this survey method.

Key words: bias, carnivores, Minnesota, population index, population trend, precision, scent-station survey, validation.

This resource is based on the following source (Northern Prairie Publication 1041):

Sargeant, Glen A., Douglas H. Johnson, and William E. Berg.  1998.
     Interpreting carnivore scent-station surveys.  Journal of
     Wildlife Management 62(4):1235-1245.

This resource should be cited as:

Sargeant, Glen A., Douglas H. Johnson, and William E. Berg.  1998.
     Interpreting carnivore scent-station surveys.  Journal of
     Wildlife Management 62(4).  Jamestown, ND:  Northern Prairie
     Wildlife Research Center Online. 
     http://www.npwrc.usgs.gov/resource/mammals/scent/index.htm
     (Version 20JAN99).

¹Northern Prairie Science Center, Biological Resources Division, U.S. Geological Survey, 8711 37th Street SE, Jamestown, ND 58401, USA
²Minnesota Department of Natural Resources, 1201 East Highway 2, Grand Rapids, MN 55744, USA

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Interpreting Carnivore Scent-station Surveys

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